I. Field of the Invention
This invention relates generally to air-accumulator and discharge devices of the type generally known as air blasters, air cannons, or blast aerators. More particularly, the present invention relates to heavy duty blast aerators of the type classified in U.S. Patent Class 222, Subclasses 2, 3 and 195 and Class 251, Subclass 30.02.
II. Description of the Prior Art
As is well known to those with skill in the art, the passage of bulk materials through conventional handling equipment is often degraded or interrupted. Typical bulk materials comprise concrete mixtures, grains, wood chips or other granular materials disposed within large hoppers or storage bins. In conventional, conically shaped hoppers, for example, bridges or arches of bulk materials often form, preventing or minimizing the orderly flow or delivery of granular materials. Often, xe2x80x9crat holesxe2x80x9d or funnels build up, and material passage is severely degraded or halted altogether. Particles of bulk material may form cohesive bonds either by adhesion due to chemical or electrostatic attraction, or particles may interlock because of horizontal and vertical compression. Such materials usually tend to cake or congeal during bulk processing. When moisture accumulates, unwanted caking tends to block flow. It is also recognized that friction between bulk material and the walls of a typical bunker or hopper in which the material is confined tends to interfere with proper flow.
Blast aerators or air cannons have long been employed to dislodge blocked or jammed bulk material. Storage bins or hoppers, for example, are often fitted with one or more high pressure air cannons that periodically blast air into the interior to dislodge caked particles, break funnels and bridges, and destroy rat holes. Bulk flow problems can temporarily be stopped by physically vibrating the hopper or container to shake loose the jammed materials. But not all materials may be dislodged in this manner. For example, large concrete bunkers may be impossible to vibrate. Materials like soft wood chips ordinarily absorb vibratory energy and must be dislodged by other methods.
Air blasters are preferred over vibrators because of efficiency. The forces outputted by blast aerators are applied directly to the material to be dislodged, rather than to the walls of the structure. Modern air blasters are also preferred over air slides, air wands, and various air screen devices which operate at low pressures. Live bottoms in hoppers or bins are limited in their effectiveness, since they may tend to create bridging or arching of material. Modern air cannons or blast aerators are intended for use as a flow stimulator against materials that are primarily moved by gravity. They are not intended to be the prime movers of such materials, and for safety purposes they should not be used to initiate the flow or movement of bulk materials unless a gravity feed is employed.
Typical blast aerators comprise a large, rigid holding tank that relatively slowly accumulate air supplied through standard, high pressure air lines available at typical industrial facilities. A special valve assembly associated with the tank includes a high volume discharge opening directed towards or within the target application. External, solenoid-activated valve assemblies are employed to periodically activates the air cannon, whereupon the large volume of air that was slowly accumulated in the holding tank is rapidly, forcibly discharged within a few milliseconds. The volume of compressed air released by a modern blast aerator strikes the bulk material at a rate over 1000 feet per second. Materials exposed to this high volume inrush are forcibly dislodged by impact. The large volume of air outputted by the aerator spreads throughout the bin or hopper, distributing forces throughout the interior that tend to homogenize and dislodge the mixture. After an exhaust blast, the actuator assembly signals the apparatus to return to a xe2x80x9cfillxe2x80x9d position, wherein the displaceable internal blast piston blocks the aerator blast output path. The cycle repeats as air that has relatively slowly accumulated again within the blaster is subsequently discharged during the next cycle.
U.S. Pat. No. 4,469,247, issued Sep. 4, 1984, and owned by Global Manufacturing Inc., discloses a blast aerator for dislodging bulk materials. The blast aerator tank has a blast discharge opening coaxially aligned with its longitudinal axis. The blast discharge assembly comprises a rigid, tubular discharge pipe comprising an internal shoulder that forms a valve seat. A resilient piston coaxially, slidably disposed within the pipe abuts the valve seat to seal the tank during the fill cycle. In the fill position the seal is maintained by a chamfered end of the piston that matingly, sealingly contacts a similarly chamfered seat portion of the valve seat assembly. A cavity at the piston rear is pressurized to close the valve by deflecting the piston. During periodic cycles, discharge occurs in response to cavity venting, whereupon the piston is rapidly displaced away from the valve seat, exposing the discharge pipe opening to the pressurized tank interior.
Similar blast aerators may be seen in U.S. Pat. Nos. 3,651,988; 3,915,339; 4,197,966; 4,346,822; and 5,143,256. Other relevant blast aerator technology may be seen in Great Britain Pat. Nos. 1,426,035 and 1,454,261. Also relevant are West German Patent 2,402,001 and Australian Pat. No. 175,551.
Global Manufacturing U.S. Pat. No. 4,496,076 teaches a method of employing a plurality of air cannons in a controlled array.
In some prior art aerator designs, the piston and valve assembly are disposed at a right angle relative to the discharge flow path. In addition, many blast aerators use a valve assembly that is mounted externally of the accumulator tank. The latter design features are seen in U.S. Pat. Nos. 3,942,684; 4,767,024; 4,826,051; 4,817,821; and 5,853,160.
U.S. Pat. No. 5,441,171 discloses a protrusion on the rear of a slidably captivated piston to help slow the piston after firing. This design does not bleed air off in a controlled fashion and in fact the protrusion does not shut off the flow of air out of the valve body.
U.S. Pat. No. 5,517,898 discloses a pneumatic cylinder in which coaxially disposed xe2x80x9cpistonsxe2x80x9d include dampening sleeves. In other words, ports are interconnected with internal passageways including stein portions of the cylinder to dampen piston movement by compressed air.
During the hundreds of thousands of repetitive discharge cycles occurring over the normal life of a typical blast aerator, critical moving parts will inevitably wear and deform. Typical aerator actuating pistons encounter extremely high stresses from heat, friction, and pressure that eventually result in component failure. As the aerator piston deforms or wears, its ability to properly seal during the critical xe2x80x9cfill cyclexe2x80x9d is impaired. In many prior art designs that portion of the piston utilized to create a seal also functions as the working surface upon which tank pressure acts to force the piston to its rearward xe2x80x9cblastxe2x80x9d position, further aggravating component stress and shortening valve life. In operation, the blast piston must rapidly travel away from the seal during the discharge cycle. As it deforms over hundreds of thousands of blast cycles however, it may lose its symmetry, and misalignment within the valve tube can slow piston travel, enlarging the blast time period and denigrating the force of the discharge.
Of course, problems with wear and tear also afflict the exhaust valve or actuator assembly that triggers the blast aerator. A variety of solutions have been proposed in the prior art for controlling blast aerator assemblies. All of the aforementioned patents disclose some means for firing the aerators. Various venting means including electrical solenoids have been provided previously. All of these are intended to periodically vent critical, internal volumes of aerators, ultimately causing a blast discharge. Many of the actuator devices cyclically facilitate subsequent tank filling after a blast. When typical blast aerators are fired, the large blast piston is partially deflected by actuator ventilation, retreating from a sealed, blocking position to open and expose the discharge passageways for a blast. In use, the actuator solenoid assemblies are subject to repetitive, stressful firings, in conditions involving heat, humidity, and constant vibrations.
The invention comprises an accessory trigger or actuator assembly for detonating blast aerators, and a blast aerator equipped with the improved system. A preferred embodiment is ideal for high temperature applications involving environmental factors such as excessive, heat, humidity, and mechanical shock. The trigger comprises a unique symmetrical and ventilated housing that mounts a miniature internal piston. The trigger piston comprises a generally cylindrical, base and an integral, generally conical head. The base comprises a circumferential groove for seating an appropriate O-ring.
A rigid, ventilated housing internally mounts a hollow, reciprocating piston. A plurality of vent orifices radially disposed about the housing periphery are normally covered by a resilient band. The band may be deflected away from the orifices in response to sufficient air pressure, thus functioning as a check valve. The captivated, generally cylindrical piston is lightweight and hollow. It""s integral, generally conical bottom is displaced into and out of contact with a mechanical valve seat within a cylinder formed internally of the housing. An air passageway through the piston is controlled by a deflectable ball forming a valve element that is captivated within a tapered chamber inside the piston. The ball valve selectively blocks various air passages through the piston by contacting an internal valve seat. This construction with internal air passageways facilitates trigger function. The base comprises a circumferential groove for seating an appropriate O-ring.
Thus a major object is to provide a lightweight, high speed trigger mechanism for activating blast aerators, air cannons and the like.
Of course a related object is to provide a blast aerator equipped with such a trigger.
A basic object is to provide a highly reliable trigger device for blast aerators or air cannon that resists high temperatures and other stresses encountered in use.
Another object is to provide a blast aerator trigger of the character described that is of minimal volume and weight.
A fundamental option is to provide a highly reliable trigger assembly for blast aerators.
A related object is to speed up control venting systems for blast aerators.
Another general object of this invention is to provide an aerator trigger assembly whose internal piston is configured for a multiplicity of tasks.
A still further basic object is to provide a blast aerator trigger of the character described that minimizes the frequency of service calls required in the field.
A further object is to provide an improved trigger that can be retrofitted to existing blast aerators and air cannons.
These and other objects and advantages of this invention, long with features of novelty appurtenant thereto, will appear or become apparent in the course of the following descriptive sections.